title: In vivo intracellular pH measurements in tobacco and Arabidopsis reveal an unexpected pH gradient in the endomembrane system.
abstract: The pH homeostasis of endomembranes is essential for cellular functions. In order to provide direct pH measurements in the endomembrane system lumen, we targeted genetically encoded ratiometric pH sensors to the cytosol, the endoplasmic reticulum, and the trans-Golgi, or the compartments labeled by the vacuolar sorting receptor (VSR), which includes the trans-Golgi network and prevacuoles. Using noninvasive live-cell imaging to measure pH, we show that a gradual acidification from the endoplasmic reticulum to the lytic vacuole exists, in both tobacco (Nicotiana tabacum) epidermal (ΔpH -1.5) and Arabidopsis thaliana root cells (ΔpH -2.1). The average pH in VSR compartments was intermediate between that of the trans-Golgi and the vacuole. Combining pH measurements with in vivo colocalization experiments, we found that the trans-Golgi network had an acidic pH of 6.1, while the prevacuole and late prevacuole were both more alkaline, with pH of 6.6 and 7.1, respectively. We also showed that endosomal pH, and subsequently vacuolar trafficking of soluble proteins, requires both vacuolar-type H(+) ATPase-dependent acidification as well as proton efflux mediated at least by the activity of endosomal sodium/proton NHX-type antiporters.
authors.affiliation: Biochemistry and Plant Molecular Biology Lab, Unité Mixte de Recherche 5004, 34060 Montpellier, France.
authors.forename: Alexandre
authors.initials: A
authors.lastname: Martinière
authors.forename: Elias
authors.initials: E
authors.lastname: Bassil
authors.forename: Elodie
authors.initials: E
authors.lastname: Jublanc
authors.forename: Carine
authors.initials: C
authors.lastname: Alcon
authors.forename: Maria
authors.initials: M
authors.lastname: Reguera
authors.forename: Hervé
authors.initials: H
authors.lastname: Sentenac
authors.forename: Eduardo
authors.initials: E
authors.lastname: Blumwald
authors.forename: Nadine
authors.initials: N
authors.lastname: Paris
mesh_terms: D017360:Arabidopsis / Q000502:physiology*; D004721:Endoplasmic Reticulum / Q000502:physiology; D006863:Hydrogen-Ion Concentration; D018892:Proton-Motive Force; D017923:Sodium-Hydrogen Exchangers / Q000502:physiology; D014026:Nicotiana / Q000502:physiology*; D025262:Vacuolar Proton-Translocating ATPases / Q000502:physiology; D014617:Vacuoles / Q000502:physiology; D021601:trans-Golgi Network / Q000502:physiology
chemical_list: D017923:Sodium-Hydrogen Exchangers; D025262:Vacuolar Proton-Translocating ATPases